The present invention relates generally to automatically closing valves which respond to pressure drops and in particular to valves adapted to be used between a fuel oil manifold and the fuel oil burner in a boiler, such as those aboard a ship. At present, when oil pressure to a boiler subsides below a predetermined level and the fires goes out, the unmonitored resurgence of oil pressure results in the fuel oil being sprayed on the hot brickwork and caused to ignite; this is generally known as "boiler flare-back". Although the concept of the present invention is particularly suited for use with fuel oil burners, the structure is not limited to one particular application and may be utilized in devices requiring a valve closure when system pressure drops to a predetermined minimum, with manual reset necessary for the reopening of the valve. A general example of pressure-responsive valves is disclosed in U.S. Pat. No. 2,749,080 to Griswold. Griswold reveals the utilization of a diaphragm positioned in a secondary chamber which is resiliently biased to close a valve whenever fluid pressure against the diaphragm falls below a predetermined level. As distinguished from the present invention, however, a resurgence of pressure will reopen the valve. Such a valve is not suited for applications requiring monitoring prior to reopening as in fuel oil burners.